There are a number of reasons why dual X-ray absorptiometry (DXA) has become a significant method to measure body composition in both clinical as well as athletic populations. The accuracy, speed, ability to measure regional as well as total body composition, as well as a method to measure muscle, fat, and bone have led to its acceptance. If the DXA does have a drawback, it is that it uses X-ray to make its measurements and thus exposes an individual to radiation during a DXA scan. I often find that people are confused about radiation, and I wanted to write this blog to help identify just how much an individual is exposed to radiation during a DXA scan.
First of all, we live in a radioactive world, and radiation is all around us. Throughout the day we are exposed to both natural and manmade sources of ionizing radiation. Natural sources include the soils and building materials as well as gamma rays from space. Manmade sources include medical X-rays and other technological applications of radioactive materials. The annual average radiation dose per person from all natural and man-made sources is about 350 mrems. The U.S. Nuclear Regulatory Commission (NRC) has established standards that allow exposures of up to 100 millirems (mrems) per year (in addition to the 350 mrems you normally receive) for members of the public and 5,000 mrems per year for those who work with and around radioactive material.
So where does DXA fall on when it comes to radiation exposure to the participant. The 3 manufactures of DXA (Hologic, Inc., GE Healthcare, and Norland at Swissray) use slightly different X-ray admitting methods so they each have a little different level of radiation exposure for the determination of total body composition. For example, for a total body scan, the Hologic Horizon A scanner exposes an individual to 0.7 mrems. The GE Healthcare iDXA scanner exposes the patient to 0.3 mrems when scanning on the standard mode; however, when the scanner uses the thick mode (used for larger individuals) the radiation exposure increases to 0.6 mrems. The Norland Elite exposes the patient to 0.02 mrems; however, this amount also increases for larger individuals. It should be noted that besides the radiation dose being different, the time of exposure for the 3 different DXA scanners is also different. Although the Hologic Horizon A uses a higher scan dose, the exposure time (113 seconds) is less than the GE Healthcare iDXA (standard mode: 436 seconds, thick mode: 796 seconds). The Norland Elite is variable given the size of the individual, but the company says that is it greater than 300 seconds.
As you can see the radiation exposure from a DXA is very low. When you compare it to other medical procedures, the closest in radiation exposure is a dental X-ray at 0.5 mrems. A chest X-ray exposes an individual to 13 mrems, while the radiation exposure of a standard mammographic study is 6 mrems. A computed tomography scan (CT) exposes you to even more radiation than an X-ray. The radiation of a standard chest CT is 74 mrems, while a head CT exposes you to about 38 mrems.
Of course, we do not get CT or X-rays on a daily basis, however, you are exposed to radiation on a daily basis form such things as wearable computers and technology, granite countertops, brick, concrete, etc. Every time you fly, you receive radiation. For example, one trip from the east coast to the west coast would expose you to about 3.5 mrems. Even humans emit some radiation. For example, sleeping next to someone for 8 hours exposes you to approximately 2 mrems. The bottom line is radiation is all around us and on a daily basis, we receive radiation.
Although one should never disregard the radiation exposure that one receives from a DXA scan, the amount is actually very small. If an individual received 4 DXA scans in a given year, the total annual radiation exposure would be less than 3 mrems from DXA scans, or less than what would be received in a flight across the U.S. In most cases, the accuracy of a DXA scan and the information gained about fat, muscle, and bone as well as being able to determine regional body composition and total body composition outweigh the low radiation exposure.
United States Nuclear Regulatory Commission. (January 31, 2020). Personal Annual Radiation Dose Calculator. Retrieved from https://www.nrc.gov/about-nrc/radiation/around-us/calculator.html
National Council on Radiation Protection and Measurements. (May 29, 2015) NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States. Retrieved from https://ncrponline.org/publications/reports/ncrp-report-160
Frame P, Kolb W. (2003) Living With Radiation: The First Hundred Years.
Mettler FA, Bhargavan M, Faulkner K, et al. (2009). Radiologic and Nuclear Medicine Studies in the United States and Worldwide: Frequency, Radiation Dose, and Comparison with Other Radiation Sources – 1950-2007. Radiology 253(2) 520-531.
About the Author
Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.